This invention relates to a brushless alternator. More specifically, it relates to an improved high-performance brushless alternator of the type having a separate exciter and rectifiers for providing a DC voltage to an alternator field winding.
The use of brushes in electricity generating equipment has several disadvantages. Initially, brushes tend to wear quickly and have a relatively short lifespan in comparison to the equipment itself. If a generator is installed in a location which prohibits easy access, it can become quite burdensome to maintain the equipment by replacing or cleaning the brushes. The use of brushes requires that the equipment be serviced regularly, whereas brushless equipment can run for substantially longer periods of time, without attention. In addition, brushes produce sparks. This prohibits their use in explosive atmospheres. The sparking can also create electromagnetic interference problems. Manufacturers have developed brushless generators to overcome these drawbacks. However, these brushless type generating devices are relatively inefficient in current output, for their size and weight, in comparison to equivalent brush generators. Some prior art brushless alternators are disclosed in U.S. Pat. Nos. 3,771,046; 3,132,296; 3,401,328; 4,041,339; 4,059,778; 3,412,271; and 1,584,253. The exciters in several of the known brushless devices are of inefficient design, resulting in limited excitation current available to the generator field coil. This relatively low excitation current capability decreases the overall generator efficiency, and also creates voltage regulation problems, particularly when the generator is heavily loaded.
Bauman et al, U.S. Pat. No. 3,034,035, describes a brushless alternator having exciter and rotor field windings combined on a single rotor. This design has the same disadvantage as conventional brushless machines in that it does not provide a large exciter-to-armature current gain. In addition, since a single set of armature plates is used for both the main and exciter coils, early saturation of the armature occurs, and therefore the output of the brushless machine is limited.
The alternator in the Braun U.S. Pat. No. 3,010,040 uses only a single pole of an exciter coil which provides only a limited coupling and current output.
Accordingly, it is an object of the present invention to provide an improved brushless alternator having high current output, while being relatively compact and lightweight.
It is also an object of the invention to provide such a brushless alternator which is of simple and economical manufacture and which is reliable in operation.